To add a sticky note (text annotation) to a PDF Document.

const doc = await PDFNet.PDFDoc.createFromURL(filename);
const page = await doc.getPage(1);

// Create the sticky note (Text annotation)
const txt = await PDFNet.TextAnnot.create(doc, new PDFNet.Rect( 10, 20, 30, 40 ));
txt.setIcon("UserIcon");
txt.setContents("The quick brown fox ate the lazy mouse.");
txt.setColor((await PDFNet.ColorPt.init(0,1,0)));
txt.refreshAppearance();
page.annotPushBack(txt);

Add or edit PDF annotations
Full code sample which shows how to add or edit PDF annotations (e.g. hyperlink, intra-document link, stamp, rubber stamp, file attachment, sound, text, free-text, line, circle, square, polygon, polyline, highlight, squiggly, caret, and ink).